1. Field of the Invention
The present invention relates to a fiber-reinforced composite material composition and a process for curing it. More specifically, it relates to a curable fiber-reinforced resin composition which is quickly curable by a safe and simple process, and which can be used for various types of molding, including hand lay-up molding, spray-up molding, resin transfer molding (hereunder abbreviated to RTM) and vacuum-assisted resin injection molding (hereunder abbreviated to VARI), and to a process for curing it.
2. Description of the Related Art
Fiber-reinforced resin compositions, which are composite materials of reinforcing fibers and resins, are known conventionally as FRPs, and are widely used for many different purposes. Of the various FRP molding processes, spray-up molding, RTM and the like require rapid curing for reasons of workability and mold cycling-up. However, spray-up molding involves normal temperature curing using a peroxide-based catalyst, and has therefore been associated with such problems as greater temperature effect, difficult adjustment of the curing time, and the need for addition of large amounts of peroxide-based catalyst for improvement of the molding cycle.
In addition, when glass fibers are impregnated with a resin by the spray method, degassing must be performed with a roller to eliminate the incorporated air bubbles, and since this step requires much man-power, recent improvements have been made such as modifications and additives to the resin composition, and thus degassing has been moving in a direction toward greater simplification. Simplification of the degassing makes possible a higher speed molding cycle, but with normal temperature curing of conventional peroxide-based catalysts, the difficulty in adjusting the curing times, due to unsatisfactory curing during winter and gelation of the resin solution during molding operations during summer, etc., have led to the problem of serious defects in the products.
On the other hand, when the spraying surface is at a near-perpendicular angle the sprayed resin composition drips before it cures, resulting in a non-uniform thickness of the product and thus leading to a lack of strength or to water leakage. It has been impossible to perfectly prevent this dripping even by rendering the resin solution thixotropic.
Furthermore, in order to increase the speed of the molding cycle with RTM, VARI, etc., it is necessary either to heat the mold or adjust the amount of the peroxide-based catalyst for normal temperature curing. For heating of the mold, it is difficult to guarantee the heat source particularly when forming particularly large molded products, and when the amount of the catalyst is adjusted it is impossible to avoid reduction in the product quality due to the difficulty of adjusting the curing time to counter unsatisfactory curing in winter and relation, during the injection operation during summer.
Methods aimed at overcoming these problems have been proposed, which employ photocuring with ultraviolet light, visible light, etc., to allow the curing reaction to take place at a lower temperature and in a shorter time (for example, H. Shreiber, Plastverarbeiter, 33 (4)404, 1982, and Japanese Unexamined Patent Publication No. 2-97503). However, when large amounts of reinforcing fibers or inorganic fillers are included, or the molded product thickness is large, curing of the interior or back side thereof with ultraviolet light or visible light has been difficult.
In addition, it is particularly difficult for simple light irradiation to accomplish curing to the interior or back side of carbon fiber-type and aramid fiber-type resin compositions which are largely impermeable to light, and for example, Japanese Unexamined Patent Publication No. 8-57971 proposes a method whereby a carbon fiber-reinforced resin composition is cured by irradiation in the presence of a near-infrared light or visible light photoinitiator or a thermal polymerization initiator; however, unless curing of carbon fiber-reinforced resin compositions by this method is carried out with a light source which generates large amounts of heat and the initiator used is capable of initiating polymerization not only by light but also by heat, it is impossible to achieve curing to the interior or back side of the composition.
In fact, in cases where sufficient usable life of the resin composition containing the initiator is required and stability of the initiator is an object, it is necessary to use an initiator which initiates polymerization at high temperatures in order to prevent decomposition of the initiator at the storage temperature, and this is a disadvantage in that curing of the composition therefore requires large light irradiation equipment with large amounts of heat generation. Also, usable reinforcing fiber materials are limited to carbon fibers, and it has not been possible to employ materials reinforced with aramid fibers or glass fibers.
In addition to this proposed method there are known polymerizable compositions containing novel polymerization initiators consisting of combinations of organic boron compounds and acidic compounds (Japanese Unexamined Patent Publication No. 6-329712, and Japanese Unexamined Patent Publication No. 8-3210), and although highly safe polymerization initiation systems have also been proposed therefor, the effect on polymerizable compounds which are used industrially, such as unsaturated polyester resins and vinyl ester resins has been inadequate, while there have been absolutely no reports of their application to FRPs mentioned above, and therefore they have been unsuitable for practical use.